75 CB360 - bad omen "yatagarasu" build

crazypj

Split personality, I fake being smart
Wish there was a 'joker' emoji ;D
I don't remember the numbers but I did post them 'somewjere' Think I worked out to inertia compared to stock so decided a 12,000rpm 'red-line' would be OK particularly as points won't let it rev reliably top much more than 11,500 8)
 
Re: 75 CB360 - bad omen "yatagarasu" build

irk miller said:
I wasn't questioning that it's lighter. Just making an observation that things weren't weighed under the same conditions between both pistons.
Yea I'm disappointed in myself I thought I was being all scientist with the digital scale. My gf was pissed I was using the kitchen scale for dirty pistons
 

onefromexile

New Member
Re: 75 CB360 - bad omen "yatagarasu" build

MiniatureNinja said:
Yea I'm disappointed in myself I thought I was being all scientist with the digital scale. My gf was pissed I was using the kitchen scale for dirty pistons
That’s not bad I used the Cmm at work to measure and inspect my head job
Port matched within a thou
Overkill
Oh and yeah my gs pistons were about less 1/4 gram off each other but I was able to remove excess casting marks on under side and got em to read exact
Worth it ??
Who knows


Sent from my iPhone using DO THE TON
 

crazypj

Split personality, I fake being smart
Re: 75 CB360 - bad omen "yatagarasu" build

MiniatureNinja said:
Yea I'm disappointed in myself I thought I was being all scientist with the digital scale. My gf was pissed I was using the kitchen scale for dirty pistons
LOL, got caught. I wait until wife is in work and 'air out' house when I do stuff like that ;)
 
Re: 75 CB360 - bad omen "yatagarasu" build

onefromexile said:
That’s not bad I used the Cmm at work to measure and inspect my head job
Port matched within a thou
Overkill
Oh and yeah my gs pistons were about less 1/4 gram off each other but I was able to remove excess casting marks on under side and got em to read exact
Worth it ??
Who knows


Sent from my iPhone using DO THE TON
I may use this scale to check that out, they are different in diameter by a couple thousandths so when I gave instructions to machine shop for boring they bored a right and left differently
One is probably lighter than the other
 

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NvgtrWiggles

New Member
MiniatureNinja said:
ran into sort of a problem and have been held up a few days - I seam to have misplaced the shim (thrust washer b) needed for the camshaft end play (part number 90484-369-000)

I am not sure if it slipped in between the cracks in my work bench but it's LOST FOREVER

problem is... everywhere I see that - well the only way to get one is to reuse the one you have.

in other news I got my head back from the shop, oversized 1mm intake and a mildly ported (match port, D shaped exhaust and matched intake boots, small sculpting done to the intake and exhaust around the valve guides and smoothed area at the seats

getting excited to get this thing together

oh, and while I was searching for the thrust washer I keep coming across a "sealing washer" (like this one) and I have no idea what it is where it goes
I have a pile of 360 engines if you need a washer. Yours for cost of shipping.
 

crazypj

Split personality, I fake being smart
Waste of time measuring top edge of piston to bore. It runs hot and expands to fill the gap.
About 10mm~15mm from base is where you measure. (depends on type and manufacturer.
I always look for the largest diameter I can find, 90 degrees to pin.
You need to use micrometer, I use inch as I don't have metric with thousandths of mm(tenthousandths of inch vernier micrometers are more commonso much cheaper than metric versions)
Most pistons are made 'surfboard' shaped on lower edge, reduces friction and promotes oil film, but, they can build up an oil wedge at very high rpm and may give a 'smokey' motor as oil rings can't cope. It's part of the reason I like OEM pistons, they were designed to work very well to a specific rpm, plus 3~4 K before oil control is a problem
 
Re: 75 CB360 - bad omen "yatagarasu" build

NvgtrWiggles said:
I have a pile of 360 engines if you need a washer. Yours for cost of shipping.
What do you mean by "pile" ? I'm always up for more parts!
 
Re: 75 CB360 - bad omen "yatagarasu" build

crazypj said:
Waste of time measuring top edge of piston to bore. It runs hot and expands to fill the gap.
About 10mm~15mm from base is where you measure. (depends on type and manufacturer.
I always look for the largest diameter I can find, 90 degrees to pin.
You need to use micrometer, I use inch as I don't have metric with thousandths of mm(tenthousandths of inch vernier micrometers are more commonso much cheaper than metric versions)
Most pistons are made 'surfboard' shaped on lower edge, reduces friction and promotes oil film, but, they can build up an oil wedge at very high rpm and may give a 'smokey' motor as oil rings can't cope. It's part of the reason I like OEM pistons, they were designed to work very well to a specific rpm, plus 3~4 K before oil control is a problem
You told me in PM how to measure and I gave those instructions to the machine shop he said that's how he does it anyway so I'm confident in the work done, the valve seats look great, he lapped them in after, 1mm oversize KPMI intakes and I'm doing the porting myself, smoothed the casting lines, d shaped exhaust, smoothed transition and matched intakes to boots
 

onefromexile

New Member
MiniatureNinja said:
I may use this scale to check that out, they are different in diameter by a couple thousandths so when I gave instructions to machine shop for boring they bored a right and left differently
One is probably lighter than the other
Well they should be slightly oval not exactly round the pistons
The bore should be exact
There is a reason I just can’t remember exactly how to phrase it


Sent from my iPhone using DO THE TON
 
Re: 75 CB360 - bad omen "yatagarasu" build

crazypj said:
Should be a little pocket rocket when done 8)
Try not to hurt yourself ;)
Me? Get hurt? I'm invincible! That's the 19 year old U.S. Marine talking

Now I'm 36 with kids... I just really wanna beat my friends CB900 with this bike I know I can do it
 
Re: 75 CB360 - bad omen "yatagarasu" build

Sonreir said:
I went with Arias on my build. 210g each. ;D

But then I broke them and swapped over to GS850s.. :(
If I remember from your HTn thread you did that because you were doing megacycles cam?
I forgot to ask what was all involved in getting that came. Why they needed a special piston, probably due to the amount of lift. I thought I would drop a megacycles cam and titanium springs in at a later date but I wont get to do that if the pistons need work too
 

crazypj

Split personality, I fake being smart
Re: 75 CB360 - bad omen "yatagarasu" build

MiniatureNinja said:
Me? Get hurt? I'm invincible! That's the 19 year old U.S. Marine talking

Now I'm 36 with kids... I just really wanna beat my friends CB900 with this bike I know I can do it
If it's the 1979~82 CB900, find somewhere with several medium to tight turns with no long straights and he'll think he's riding a three legged camel (*if it's one of them, he is ;D )They are a heavy lump to hustle through a series of twisties ;)
 
Re: 75 CB360 - bad omen "yatagarasu" build

crazypj said:
If it's the 1979~82 CB900, find somewhere with several medium to tight turns with no long straights and he'll think he's riding a three legged camel (*if it's one of them, he is ;D )They are a heavy lump to hustle through a series of twisties ;)
it's an 82 and it's been "cafe'd" out but as i learn about doing mine, not very well... just basic "cafe racer" stuff and no performance gains. much lighter than stock I imagine
where we raced last time is close to what you described, but there are 2 main sections of long straights he just pulled away so fast on

question, how much blu-tack should I get to check valve clearance? and can I do it with no valve springs in just valves closed and everything torqued down?
 
Re: 75 CB360 - bad omen "yatagarasu" build

NvgtrWiggles said:
6 mostly complete engines.
Cool, I'd buy a spare complete! I'm always getting spare parts on Ebay just in case


Just about to do the valve clearance test on the engine when I get back from the store with some blu-tack or something similar. I assumed staples would have it. They don't.

Although I really dont know what to do if they are too close... maybe order new gasket?
 

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teazer

Active Member
DTT BOTM WINNER
onefromexile said:
Well they should be slightly oval not exactly round the pistons
The bore should be exact
There is a reason I just can’t remember exactly how to phrase it


Sent from my iPhone using DO THE TON
Pistons are thinner from side to side compared to front to back. That's to reduce viscous drag in the same way that slipper pistons are designed but at a much lower cost of manufacturing.

They are also smaller at the top where they get hotter and expand more than at the bottom of the skirt where they stay cooler and expand less.

Pistons also rocks lightly and the bottom 1/2" or so tends to be more worn and that's why they tell you to measure a little way up from the bottom of the skirt.

And yes, pistons do tend to be slightly different from one to another, so your machine shop should always bore each side to match a particular piston and they should come back marker 1,2 or something similar.
 

teazer

Active Member
DTT BOTM WINNER
MiniatureNinja said:
If I remember from your HTn thread you did that because you were doing megacycles cam?
I forgot to ask what was all involved in getting that came. Why they needed a special piston, probably due to the amount of lift. I thought I would drop a megacycles cam and titanium springs in at a later date but I wont get to do that if the pistons need work too
"hotter" cams usually have more lift and more duration (held open for longer), so they tend to need more piston to valve clearance than a stock cam. Some motors have enough clearance to get away with hotter cams, but some are tight stock and need valves to be recessed slightly or pockets cut in the piston crowns - or both if you mill the head and fit race cams.

The process is simple but tedious. You build the motor with light valve springs and gently turn it over to see when the valves touch the pistons and then back off the valve adjustment until it just turns over. Then you calculate how much valve clearance you have when the valves are closed and that's a starting point for how much to cut the pistons or head.

You want about 40 -60 thou clearance between valve and piston at the point they are closest to each other and obviously there must be clearance between the valves which can be an issue when fitting large valves.

Repeat until you have sufficient clearance and then assemble the motor for real.

With race motors, that's just how it goes. With mid cams there may be sufficient clearance if you get lucky. Sometimes the motor clicks as it runs when pistons touch the valves and then it's motor out time again.
 

crazypj

Split personality, I fake being smart
Use modeling clay or Play Doh to check clearance. Michaels, ToysRUs, etc With pistons, the extra mass around gudgeon pins expands more than thinner sections which is another reason 'sides' are reduced diameter. If your pistons are sticking out 0.010", you use a 0.050" head hasket or next thicker one. You want around 0.035"~0.040" piston to head clearance
 

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